1. Field of the Invention
The present invention relates generally to image sensor packaging. More particularly, the present invention relates to an optical cover plate for image sensor wafer level package and fabrication method thereof. The invention optical cover plate includes an improved dam structure. Further, the invention provides an image sensor package using the same and fabrication method thereof.
2. Description of the Prior Art
With the development and popularity of electronic products such as digital cameras, mobile phones, personal computers and scanners, the image sensor devices have been widely used in various fields. The commonly used solid-state image sensor devices can be generally categorized into two types: charge-coupled device (CCD) and CMOS image sensor. As known in the art, the CMOS image sensors are compatible with semiconductor manufacturing process to achieve low-cost manufacturing. The CMOS image sensors also provide advantages such as small size, low-voltage, low power consumption.
Basically, a CMOS image sensor device is comprised of an optical cover plate and an image sensor die. The optical cover plate comprises a transparent body and a dam structure, wherein light can pass the transparent body. The dam structure is typically formed on an inner side of the transparent body facing the image sensor die. The dam functions as a spacer to maintain a space between the transparent body and the image sensor die. The dam structure, the transparent body and the image sensor die together constitute a cavity to protect the image sensing area on the image sensor die. After incident light passes the transparent and reaches the image sensing area, it can be effectively converted into digital signal.
However, the aforementioned prior art package structure, when used in different circumstances, is subject to peeling. The peeling typically occurs at the interface between the dam structure and the image sensor die and/or the interface between the dam structure and the transparent body because of humidity, stress even the effects of temperature, thereby affecting the reliability of component packaging. In addition, during the back-end stress test such as high accelerated stress test (HAST), temperature-humidity storage test (THS) or other reliability tests, it has been found that the dam structure itself may absorb moisture, resulting in high tensile stressed component packaging, which reduce production yields. Further, the color of the dam structure is usually green, there would be image color cast (slightly greenish) issue, which reduces the image quality. From this, the prior art still has technical issues which need further improvement.